The present invention relates to a device for lateral alignment of a sheet in a sheet processing machine, in which the sheet is movable essentially across its direction of transport into an alignment position and the sheet is movable into the aligned position by a side pulling device.
Before a sheet can be processed in a printing press or a folding machine, it must be aligned to the machine inlet. Side pulling devices which convey the sheet to be processed against a side stop, whereby each sheet at the inlet of the machine assumes the same lateral position, are known to achieve this object. Such a side pulling device has, for example, a suction box which is movable across the direction of transport of the sheet, draws the sheet to be aligned by suction and then conveys it toward the side stop. German Patent Application No. 199 10 688 A1 describes a side pulling device which has two side stops and two pull bars to align the sheet to one of the stops both on the right and on the left. Also in this case suction is applied to the two pull bars, so that they can exert a holding force on the sheet to be aligned. Furthermore, the pull bars are each located in the side edge zone of the sheet to be aligned, in a feed table opposite one another below the transport level of the sheet. If the sheet is to be aligned to the right-hand stop, the right-hand pull bar is activated, and the sheet is moved to the right-hand stop. If the sheet is to be aligned to the left-hand stop, the left-hand pull bar is activated, and the sheet is moved to the left-hand stop. Thus, the sheet is handled and aligned by one or the other pull bar depending on whether it is to be aligned to the right or to the left. However, only the pull bar whose side has been selected manually is always active, i.e., all sheets are transported either to the right or to the left. This device for laterally aligning sheets has the disadvantage that only one pull bar is activated at any given time. Although there are two pull bars, one pull bar must do the entire alignment job by itself. The sheet is held fast using a single pull bar; therefore additional pressure rollers must be used to prevent the sheet to be aligned from fluttering to the side where it is not guided.